High efficiency photovoltaic cells with self concentrating effect

ABSTRACT

Novel structures of photonics devices (e.g. photovoltaic cells also called as solar cells) are provided. The Cells are based on the micro (or nano) structures which could not only increase the surface area but also have the capability of self-concentrating the light incident onto the photonics devices. Using of such structures, it is possible to achieve significant performance improvement. For example, if such structures are used in the photovoltaic cells, large power generation capability per unit physical area is possible over the conventional cells, and have enormous applications such as in space, in commercial, residential and industrial applications. Such structures are also beneficial to other photonics devices such as photodetector to enhance the performance.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/827,015 filed Sep. 26, 2006, and also patent application Ser. No.11/859,742, filed on Sep. 22, 2007.

FIELD OF INVENTIONS

This patent specification relates to structures of photovoltaic cells(hereafter mentioned as also “solar cells”). More specifically, itrelates to photovoltaic cells comprising with structures for increasingthe junction area and also for absorbing broad solar spectral forincreasing power generation capability per unit area. This also relateswith the photovoltaic cells having elf amplifying capabilitiesconcentrating (increasing) light intensity incident on its surface. Thisalso relates to photovoltaic cells comprising with nano-scaled blocks.These photovoltaic cells can be used in commercial, residential, andalso industrial application for power generation.

BACKGROUND OF THE INVENTIONS

Photovoltaic cells where light is converted into electric power havebeen prevailing in a wide range of application fields such as consumerelectronics, industrial electronics, and space exploration. In consumerelectronics, photovoltaic cells that consist of materials such asamorphous silicon are choices for a variety of inexpensive and low powerapplications. Typical conversion efficiency, i.e. the solar cellconversion efficiency, of amorphous silicon based photovoltaic cellsranges between ˜10% [Yamamoto K, Yoshimi M, Suzuki T, Tawada Y, OkamotoT, Nakajima A. Thin film poly-Si solar cell on glass substratefabricated at low temperature. Presented at MRS Spring Meeting, SanFrancisco, April 1998.]. Although the fabrication processes of amorphoussilicon based photovoltaic cells are rather simple and inexpensive, onenotable downside of this type of cell is its vulnerability todefect-induced degradation that decreases its conversion efficiency.

In contrast, for more demanding applications such as residential andindustrial solar power generation systems, either poly-crystalline orsingle-crystalline silicon is the choice because of more stringentrequirements for better reliability and higher efficiency than theapplications in consumer electronics. Photovoltaic cells consisting ofpoly-crystalline and single-crystalline silicon generally offer theconversion efficiency ranging ˜20% and ˜25% [Zhao J, Wang A, Green M,Ferrazza F. Novel 19.8% efficient ‘honeycomb’ textured multicrystallineand 24.4% monocrystalline silicon solar cell. Applied Physics Letters1998; 73: 1991-1993.] respectively. As many concerns associated with asteep increase in the amount of the worldwide energy consumption areraised, further development in industrial solar power generation systemshas been recognized as a main focus. However, due to high cost ($3 to$5/Watt) of today's Si-based solar cell, this Si-solar cell is not yetwidely accepted as an alternative source for the energy solution.

Group II-VI compound semiconductors, for example CdTe and CdS, have beeninvestigated in the context of having industrial solar power generationsystems manufactured at a lower cost with maintaining a moderateconversion efficiency, resulted in a comparable conversion efficiency˜17% [Wu X, Keane J C, Dhere R G, DeHart C, Duda A, Gessert T A, AsherS, Levi D H, Sheldon P. 16.5%-efficient CdS/CdTe polycrystallinethin-film solar cell. Proceedings of the 17th European PhotovoltaicSolar Energy Conference, Munich, 22-26 Oct. 2001; 995-1000.] to thosefor the single crystalline silicon photovoltaic devises, however toxicnatures of these materials are of great concerns for environment.

Group I-III-VI compound semiconductors, such as CuInGaSe₂, have beenalso extensively investigated for industrial solar power generationsystems. This material can be synthesized potentially at a much lowercost than its counterpart, single crystalline silicon, howeverconversion efficiency, ˜19%, comparable to that of single crystallinesilicon based cells can be obtained, so far, by only combining with thegroup II-VI compound semiconductor cells [Contreras M A, Egaas B,Ramanathan K, Hiltner J, Swartzlander A, Hasoon F, Noufi R. Progresstoward 20% efficiency in Cu(In,Ga)Se polycrystalline thin-film solarcell. Progress in Photovoltaics: Research and Applications 1999; 7:311-316.], which again raise issues associated with toxic natures ofthese materials.

A type of photovoltaic cells designed for several exclusive applicationssuch as space, where the main focus is high conversion efficiency andcost is not the main factor. Generally, this solar cell consists ofgroup III-V semiconductors including GaInP and GaAs. Synthesis processesof single crystalline group III-V are in general very costly because ofsubstantial complications involved in epitaxial growth of group III-Vsingle crystalline compound semiconductors. Typical conversionefficiency of group III-V compound semiconductor based photovoltaiccells, as these types of photovoltaic cells are intended to be, can beas high as ˜34% when combined with germanium substrates, another veryexpensive material [King R R, Fetzer C M, Colter P C, Edmondson K M, LawD C, Stavrides A P, Yoon H, Kinsey G S, Cotal H L, Ermer J H, Sherif RA, Karam N H. Lattice-matched and metamorphic GaInP/GaInAs/Geconcentrator solar cells. Proceedings of the World Conference onPhotovoltaic Energy Conversion (WCPEC-3), Osaka, May 2003; to bepublished.], usually more than 10 times than the conventional Si-solarcell.

All types of photovoltaic cells in the prior arts described above, nomatter what materials a cell is made of, essentially falls into onespecific type of structure, which usually limits is power generationcapability. Usually flat pn-junction structure is used in conventionalsolar cells (FIG. 1A). Shown in FIG. 1A is a photovoltaic cellcomprising a thick p-type semiconductor layer 101 and a thin n-typesemiconductor layer 102 formed on an electrically conductive substrate100. A pn-junction 103 is formed at the interface between the p-typesemiconductor layer 101 and the n-type semiconductor layer 102. Incidentlight 104 entering the cell generate electron-hole pairs after beingabsorbed by the p- and also n-type semiconductor layers 101 and 102. Theincident light generates electrons 105 e and also holes 105 h in theregion near the pn-junction 103 and also 106 e and 106 h in the regionfar from the pn-junction 103. The photo generated electrons (and holes)105 e and 106 e (hereafter considering only electronics, i.e. minoritycarriers in p-type semiconductors, and the same explanation isapplicable for holes, minority carriers in n-type semiconductors, also)diffusing toward the pn-junction 103 and entering the pn-junction 103contribute to photovoltaic effect. This is also vice versa for theholes, existing as minority carriers in n-type semiconductor 102. Thetwo key factors that substantially impact the conversion efficiency ofthis type of photovoltaic cell are photo carrier generation efficiency(PCGE) and photo carrier collection efficiency (PCCE).

The PCGE is the percentage of the number of photons entering a cell andcontributing to the generation of photo carriers, which needs to be,ideally, as close as 100%. On the other hand, the PCCE is the percentageof the number of photo-generated electrons 105 e and 106 e reaching thepn-junction 103 and contributing to the generation of photocurrent. Fora monochromatic light, the PCGE of ˜100% can be achieved by simplymaking the p-type layer 101 thicker, however, electrons 106 e generatedat the region far away from the pn-junction 103 cannot be collectedefficiently due to many adverse recombination processes that preventphoto generated carriers from diffusing into the pn-junction 103, thusthe basic structure of current photovoltaic cells has its own limitationon increasing the conversion efficiency. As the minority carrier travelthrough the semiconductors, the longer the life-time, the less therecombination, which makes the higher the conversion efficiency.Usually, using of thicker and high quality wafer, the conversionefficiency of conventional solar cell can be increased to some extendmentioned earlier. However, this makes the solar cell costly andheavier. In addition to increase the collection efficiency, theabsorption of the broad solar spectrum also increase the conversionefficiency.

Furthermore, increasing of the intensity of the solar spectrum helps toalso increase the conversion efficiency, thereby increasing the powergeneration capacity. Conventionally, using of the concentratorseparately with solar cell is used to increase the conversionefficiency. It requires additional component with solar cell toconcentrate the solar spectrum.

It is highly desirable to have the solar cell structure having (a) highPCCE which is independent to the substrate thickness, (b) the ability ofabsorption of broad solar spectrum, and (c) self concentratingcapability to increase the intensity of solar spectrum incident per unitarea.

FIG. 1B shows typical monochromatic light intensity behavior inside thesemiconductor, and the light intensity p at certain depth x can beexpressed as p(x)=P₀exp(−αx), where P₀ is the peak intensity at thesurface and α is the absorption co-efficient of the semiconductor inwhich light is entering. As shown in FIG. 1B, the light intensitybehavior 108 inside bulk semiconductor is exponential. Carriers (notshown here) generated due to light flux 112 absorbed by pn-junction isonly drifted by junction field and can be collected efficiently.Whereas, carriers 106 e and 106 h generated due to absorption oflight-flux 110 by semiconductor region 101 are diffused to alldirection. Only those which are generated closer (distance equal to orless than the diffusion-length of the semiconductor) to pn-junction, canbe collected. Those carriers which are generated far away (distancelonger than the diffusion-length of the semiconductor) from pn-junctionare recombined and lost. The light flux 112 is usually lost either bygoing out or absorbed by the substrate. Both PCGE and PCCE are mainlydependent on material and structure of the photovoltaic cells, andtoday's photovoltaic cells are structured in such a way that (a) wideranges of solar spectrum cannot be absorbed due to its materiallimitation, and (b) photo carrier's collection efficiency is lower dueto its inherent structure. For example, it is found that typicalconversion efficiency of today's crystal-Si based solar cell is ˜18%.Wavelengths of solar spectrum spreads from <0.1 to 3.5 μm in which Sican only absorb ˜0.4 to 0.9 μm of light. ˜50% of light belong to solarspectrum can not be absorbed by Si, due to have its inherent materialproperties. The rest of 32% are lost due to (i) recombination ofphoto-generated carriers and (ii) losing of light which is 112 as shownin FIG. 1B, and these two factors are structure dependent. If we couldreduce these two factors, ˜50% conversion efficiency can be achievedeven in Si-based solar cell. If we could capture different wavelengthsof light belonged to solar spectrum by utilizing different materialsystems or nano-material systems, we could increase the conversionefficiency ideally close to 100%. Furthermore, if the solar cell(photovoltaic cell) detection capability can be extended toinfrared-spectrum, then the cell can produce electrical energy not onlyduring day (while sun is present), but also at night (when differentinfrared is present). Besides, today's solar cell material is not highlyradiation-tolerant. In space application specially, photovoltaic cellsshould have a structure and material systems, which could generatehigh-power per unit area and also to highly radiation tolerant. Toincrease the conversion efficiency (ideally close to 100%), it would bedesirable to have photovoltaic cell structures (a) which has largersurface area to volume ratio to capture all the photons (at specificwavelength) entering the cell and a pn-junction that is located at asclose to the photo absorption region as possible, (b) amplifyingcapabilities by concentrating the light incident to its surface, and (c)structure comprising with the material systems having photo responses atdifferent spectrum to efficiently cover a wide range of spectrum oflight that enters a photovoltaic cell. It would be further desirable tohave solar cell which could generate electric power in both day andnight.

In addition to conversion efficiency, cost-effective manufacturing isalso another factor requiring some focus. In today's solar cell,high-cost is also one of the main factor in addition to issue of lowconversion efficiency. It is found that more than 90% of solar cell issilicon (Si) based solar cell in which crystal silicon (Si) wafer is thebased material, and the rest of others are thin-film based solar cell.In manufacturing of Si-based solar cell, more than 50% of cost isoriginated from Si-wafer cost and the rest are from other cost such asprocess and integration. Usage of less silicon for the fixed conversionefficiency would help to reduce the power generation cost. It is highlydesirable to focus onto the less usage of Si (to reduce the wafer cost)at the same time while increasing the conversion efficiency.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide the structuresof the photovoltaic cells, which could have high power generationcapability per unit area over conventional counterpart, mentioned as theprior arts.

According to this invention, it is an object to have an photovoltaiccell structure having self concentrating capabilities to amplify thesolar spectrum incident onto its surface.

According to this invention, it is an object to reduce thecarriers-recombination and also to increase the absorption of the lightby increasing the effective junction area, which increases thephoto-generated carriers.

According to this invention, it is an object to increase the absorptionbandwidth of solar spectrum to increase the conversion efficiency.

It is an object providing solar cell structures based on nano-scaledblocks structures which is formed on the base substrate. The pn- orSchottky junction are formed with nano blocks, generating built-inpotential by which photo generated electrons and holes are swept away,leading to photovoltaic effect.

Alternatively, the base substrate or carrier substrate could be formedin micro-nano blocks (structures) by either molding or etching process,and the junction is formed utilizing the similar semiconductor or twodifferent type of semiconductors deposited on the micro-nano blocks. Thebase or carrier substrate could be semiconductor, metal or dielectricmaterial. The pn- or Schottky junction are formed with nano-blocks,generating built-in potential by which photo generated electrons andholes are swept away, leading to photovoltaic effect.

It is an object to increase the surface area to increase the incidentlight intensity per unit its base area.

It is an object providing various solar cell structures based ontrapezoidal, pyramid, cone, or cylindrical to increase the ratio ofjunction area to the volume, to increase the conversion efficiency

According to this invention, the supporting substrate can be Si, CdTe,Cu, GaAs, InP, GaN, glass, polymer, ceramics, metal foil, Ge, C, ZnO,BN, Al₂O₃, AlN, Si:Ge, CuInSe, II-VI and III-V.

It is also object to form the structure made from electronics materialson which semiconductor pn, schotky, or MIS junction can be forced andthat electronics materials can be formed on the base substrate like Si,Ge, metal-foil, or glass to make the low-cost.

It is also another object of this invention to provide the structures ofthe photovoltaic cells which can capture most of the wavelengthsbelonged to solar spectrum and can provide >80% conversion efficiency.

It is also another object of this invention to provide the structures ofthe photovoltaic cells which can generate the electric power in both dayand night.

It is also another object of this invention to provide low-costmanufacturing process for the photovoltaic cell for making.

This invention offers to achieve ideally >50% of conversion efficiencyutilizing Si— materials and >80% of conversion efficiency for othermaterials. The main advantages of these inventions are that today'smatured process technologies can be used to fabricate the photovoltaiccell which has the power generation capability a few order and beyond ascompared with that of conventional photovoltaic cell.

Other objects, features, and advantages of the present invention will beapparent from the accompanying drawings and from the detaileddescription that follows below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail in conjunction with theappended drawings wherein:

FIG. 1A is the schematics showing the cross-sectional view of aconventional photovoltaic cell structure and FIG. 1B is the schematicshowing the light penetration as a function of the solar cell depth.This is the explanatory diagram showing the prior-art of today'sphotovoltaic cell and the light intensity behavior inside semiconductormaterials.

FIGS. 2A and 2B are the schematics showing the top and cross-sectionalviews of photovoltaic cell based on the cone(pyramid)-structure to showthe benefit of the invention, in accordance to the present invention.

FIGS. 2C and 2D are the cross-sectional views as seen from A-A′ sectionof the FIG. 2A to show the physical parameters used in the descriptionof the preferred embodiment.

FIGS. 3A and 3B are the schematics showing the cross-sectional views asseen from A-A′ section of FIG. 2A and also showing the effect of othernearest neighbors-pyramid blocks in total effective light, incident toits tilted side, in accordance to the present invention.

FIG. 3C is the cross-sectional view of the photovoltaic cell made fromtrapezoidal blocks showing the effect of nearest neighbor-blocks effectand also showing their different light components incident andtransmitted to the tilted side.

FIG. 3D is the schematic showing cross-sectional view of thephotovoltaic cell comprising with trapezoidal blocks to show theamplifying or concentrating of the light intensity, incident on to thegap (G) region in between two blocks,

FIGS. 4A and 4B are the schematics showing cross-sectional views of thephotovoltaic cell along with their physical parameters and the estimatedconversion efficiency. Only closet surrounding block-effect isconsidered in estimating the conversion efficiency.

FIGS. 5A, 5B, and 5C are the schematics showing cross-sectional views ofvarious structures for photovoltaic cells according to this invention.

FIGS. 6A, 6B, and 6C are the cross-sectional views of variousphotovoltaic cells formed on the electronic materials according to thisinvention, wherein the structures are similar to those as described inFIGS. 2 and 5A.

FIGS. 7A, 7B 7C, and 7D are the cross-sectional views of photovoltaiccells made from thin film and formed on the electronic materialsubstrate according to this invention.

FIG. 8 is the cross-sectional view of a thin-film based photovoltaiccell formed on the substrate acting as the carrier substrate accordingto this invention, wherein

FIG. 9 is the schematic showing the cross-sectional view of photovoltaiccell structure based on the photochemical material in accordance to thepresent invention.

DETAILED DESCRIPTION

According to this present invention it is our object providing severalphotovoltaic cell structures which have (a) capability of higher surfacearea to volume, (b) self concentrating capability, (c) absorption ofbroad spectrum, and (d) pn-junction very close to the surface. These allcapabilities would help to increase conversion efficiency as highas >60%. Before proceeding to give detail explanation of thephotovoltaic cell structure and their manufacturing, various structuresincluding simulation results are given to show the benefits of theincreasing the surface area (equivalent to junction area) andself-concentrating capability in the photovoltaic cell.

FIGS. 2A and 2B are the schematics representing the cone (orpyramid)-type structure 202 formed with the micro (or nano) blockstructures. The cone-structures are formed with specified pitch and basewidth m, and height h. They are formed onto the substrate 200.Alternatively, cone-structure 202 can be part of the substrate 200. InFIG. 2A, n×n number of the cone-structure 202 are arranged in a×a sizedsubstrate 200 with thickness t. It is assumed that if we could make then×n number of cone-like structure 202 on the a×a-base-area, it willincrease the surface area. This indicates that the increment of thesurface area in the proposed cell is higher than that of compared withthe conventional photovoltaic cell which is usually flat. As shown inFIGS. 2C and 2D, consider the gap between two pyramids (or cone) is G,base width is 2b (=m), and pitch of the pyramid arranged on the base, is2b+G. The maximum (b_(max)) base width is 2b+G/2 and minimum base width(b_(min)) is zero (0). Pyramid height is considered to be h. As theheight varies, the angle α also varies. The angle of the tilted sidewith respect to the base is a α. The maximum attainable angle is 90degree and minimum angle is α′, as shown in FIG. 2C.

By varying the tilted angle α with adjusting of the height h, theintensity of solar light incident onto the tilted side and the gap, canbe changed. FIGS. 3A and 3B are the schematics showing how solar lightis reflected and change their direction after incident onto the proposedcell structure, as explained in FIG. 2. As shown in FIG. 3A, if thelight intensity l 300 (from solar) is incident onto the side 306, whoseangle is α with respect to the base 308, the light transmitted into thecell l′ from the tilted side 306 is equal to l cos α and reflected lightR=l(1−cos α). When the angle α′ is minimum (see FIG. 2D), the maximumtransmission of the solar light into the cell is possible from thetilted side 306.

Several reflections and transmission components are expected as shown inFIG. 3B, while solar light incident onto the tilted side 306 of onepyramid 310 (for example) and also its closet pyramid (or cone) 312.Assuming three components of transmitted lights into the cell from thetilted side, due to incident to close neighbors, first transmissioncomponent 314 is due to its own light l which is 300, and secondtransmitted component 316 is due to its own reflected light component301 just after reflection from other pyramid 312 located very close toit. Third transmitted component 318 is due to the reflected light 303from nearest pyramid 312. The first, second, and third light components314, 316, and 318, respectively can be expressed as,First component: l×cos α  (1)Second component: (l×cos α)/(1−(1−cos α)²)  (2)Third Component: (l×cos α(1−cos α))/(1−(1−cos α)²)  (3)

Where, l is the light intensity per unit area and α is the tilted side206 angle with respect to base 308. Three components (314, 316, and 318)are only considered. Other order of reflection components alsotransmitted and they are very minimal as compared with those of threecomponents mentioned. Tilted side 306 is not only higher surface areathan the base (according to the Pythagorean Theory). Increasing surfacearea with comparable light intensity incident and transmitted to thetitled surface having larger area than that of base area (like flatcell) will help to increase the carrier generation.

FIG. 3C the schematic showing how solar light is reflected and changetheir direction after incident onto the trapezoidal shaped structure.The explanation and numeral as used in FIGS. 3A and 3B are the same forFIG. 3C, so that repeated explanation is omitted here. Only differenceis that the trapezoidal shaped structures 320 and 322 and the top base324 are used in FIG. 3C. The light component transmitted to the cell andreflection due to the tilted side 306, as explained in FIG. 3B is alsothe same in the case of FIG. 3C.

In pyramid or trapezoidal structures as explained in FIGS. 3A thru 3B,tilted side 306 has the same effect and the transmitted light componentsare the same for the same height of h. Light component l (300) incidenton to the flat surface for example on the open top surface (for the caseof FIG. 3C) 326 and the light component l′ 328 incident on the flatsurface created due to the gap 330 between two trapezoids 320 and 322,are different in intensity. The intensity l′ of light 328 incident on tothe flat surface 330 located in between two trapezoids 320 and 322 ishigher than those l of light 300 incident onto the top-flat surface 326(e.g. top surface of FIGS. 3C and 3D). The light is concentrated andincident in between the trapezoids due to the multiple reflection beamsfrom tilted side 306 which creates the angle α with respect to the base308. The effective light beams intensity, incident onto the surface 330located in between two trapezoids 320 and 322 is dependent onto theangle α. The intensity of light incident onto the opening surface 330 isdependent onto the angle α, the trapezoids height h, and the gap G.

Covers on efficiency for the structure as shown in FIG. 3D is performedfor the three variation of three structures as shown in FIG. 4A, thetilted sides of 406 a, 406 b, and 406 c. The tilted angles and the gapsbetween two trapezoids (not shown here) are changed for the threestructures as shown in FIG. 4A. Changing the tilted angle changes thegap between two trapezoids (not shown here) for the fixed height of thetrapezoids. The distance between center and the edge of the trapezoidsis considered here as X, and the X changed for estimating the conversionefficiency were D/2, D/4, and D/16, where D is the flat width of the topopening surface 426. FIG. 4B are the results for the photovoltaic cellbased on to then trapezoids structures of having three different angle.Results has been compared with that of the conventional photovoltaiccell (as shown in FIG. 1) having the flat surface. Noted here that theestimated results is for the Si—PV having substrate thickness of 350 μm,width (D) of trapezoids open top open surface and the gap (G)considering vertical cylindrical case, are 0.3 μm. The results showedthat higher conversion efficiency over 40% could be achieved for all thetrapezoidal structures, as shown in FIG. 4A. More higher conversionefficiency is also expected once the all parameters such as cell'sstructural and physical parameters, substrate parameters are optimized,Higher conversion as compared with the conventional photovoltaic cell ispossible due to increasing of the surface area of the photovoltaic celland also increasing of the solar spectrum intensity by selfconcentrating effect, as explained in FIGS. 3A, 3B, 3C, and 3D.

Increasing of the conversion efficiency for the fixed exposed areautilizing of the trapezoidal structure help to increase of the highershort circuit current as compared with that of the conventionalphotovoltaic cell of having flat surface. If the area increases, thenumber of the trapezoids are also increased and the short circuit willbe increased tremendously. The conversion efficiency is expected toincrease for all vertical structures such as the cylindrical,trapezoidal cone or pyramid) etc. FIGS. 5A, 5B, and 5C are theschematics of the photovoltaic cells made from the trapezoids,cylindrical, and pyramid structure according to this invention. They areuniformly arranged on the substrate 500. Each cell comprising of thedifferent structure. For example, cell can be comprised with trapezoidsstructure 502 a, cylindrical structure 502 b, or trapezoidal originatedfrom cylinder 502 c etc. Alternatively cell can be comprised with mixingof two or all, convenient to manufacturing process. In each cases, nnumber of the structures (e.g. trapezoids, cylindrical etc) are arrangedin a×a sized substrate. For each cases, the ratio of the surface area tothe total base area of a×a is increased with reducing of their sizes. Inall cases as shown in FIGS. 5A, 5B, and 5C, increasing the ratioindicates the increasing of the conversion efficiency as compared tothat of the conventional cell having flat surface.

According to a preferred embodiment illustrated in FIG. 6A, shown is aphotovoltaic cell comprising plurality of micrometer(s)-scaled pyramid601 formed on the supporting substrate 600 (after having groove). Themicrometer(s)-scaled pyramids 601 can have metallic electricalconduction, p-type or n-type semiconductor electrical conduction. Themicrometer(s)-scaled pyramids are further surrounded by an electronicmaterial 602 having metallic electrical conduction, p-type or n-typesemiconductor electrical conduction. The electronic material 602 can beseparated material or electronics materials of p or n type formed inside601 and 600. The electronic material 602 and the supporting substrate600 are further electrically connected to electrodes 603 a and 603 b,respectively. The electrode 603 a and 603 b are intended to serve ascommon electrodes that connects all pyramids 601. The electrode 603 a isprovided for the electronic material or junction 602. The electrode 603a can be transparent (not shown here) and can be formed on theelectronic material or junction 602. The interface between themicrometer scaled pyramids 601 and the electronic material (or junction)602 form pn- or Schottky junctions where built-in potential for bothelectrons and holes is generated.

According to this invention, alternatively the micrometer(s)-scaledpyramids 601 can be formed on separate substrate (not shown here), andthe electrode 603 b can be formed on the substrate to have commoncontact for each micrometer(s)-scaled pyramids 601, necessary forcreating junction. In way of an example not way of limitation, thenanometer(s) or micrometer(s)-scaled pyramids 601 can be made of n-typesemiconductor and the electric material 602 that on or surrounds themicrometer(s)-scaled pyramids 601 can be made of p-type semiconductor.Incident light 604 enters the photovoltaic cell through either theelectrode 603 a (not shown here) or on the material or junction 602. (InFIG. 6A, the incident light enters the photovoltaic cell through theelectrode 602). The incident light 604 travels through pyramids 601,electronic material (n or p-type) or junction 602, and the substrate600. As the incident light 604 travels through the micro-scaled pyramids601, and electronic material 602, a numerous number of electrons (notshown here) are generated in the region near the electrode 603 a.Portion of light 604 which passes through the valley portion of thepyramids where the electronic material 607 is used for passivation ormake the junction in between micro-scaled pyramids 601 are traveledthrough the electronic material 602 and the supporting substrate 600 andgenerates electrons (not shown here). Some of which generated closer toelectronic material 602 are collected and some of which are generated inthe region far from 602 are recombined and lost. It should be pointedout that electrons are apparently generated all over the region alongthe thickness of the electric material or junction 602. In addition, asthe incident light 604 travels through the micrometers)-scaled pyramids601, a numerous number of holes (not shown here) are generated in thepyramids 601 and in the substrate 600, respectively. It also should bepointed out that holes are apparently generated all over the regionalong the thickness of the micrometer(s)-scaled pyramids 601 and thesubstrate 600. Photo-generated electrons generated in the electronicmaterial 602, pyramids 601, and substrate 600 diffuse towardpn-junctions, created at the interface between the micrometer(s)-scaledpyramids 601 and the electronic material or junction 602, and also atthe interface between the electronic material 602 and substrate 600. Atthe pn-junctions, the electrons and the holes are swept away by built-inpotential, thus photovoltaic effects set in. As mentioned earlier, beam604 incident on to the tilted surface 608 will have almost the intensitycloser to the solar spectrum. As the surface area is increased due toutilize of the pyramid structure, the conversion efficiency isincreased. As there are no gaps located in between two pyramidstructures, beam concentration (considering the fixed base area) is onlyexpected on the tilted surface.

Unlike conventional solar cell, the solar cell, as shown in FIG. 6A, haspn-junction in the regions of all sides 608 of the pyramids 601. Thepn-junction formed on the side 608 of pyramids having height h hassurface area, dependent on the height h of the pyramids 601. The light604 travels perpendicular to the direction of the pn-junction formedacross side 608 of the pyramids and most of the light flux incident onthe pn-junction are absorbed and most of the photo-generated carrierscan be collected. The light 604 travels perpendicular to thepn-junctions formed at the side 608 of the pyramids 601. Most of thelight flux incident onto the sides can also be absorbed, and thecarriers generated by the light 604 can be collected withoutrecombination (ideally). It is apparent that utilizing the solar cell asshown in FIG. 6A can (i) reduce the recombination, (ii) increasing thesurface increasing the more intensity for the fixed base area, and (ii)absorb all photo flux as transmitted to the semiconductor, therebyincreasing the conversion efficiency.

According to a preferred embodiment illustrated in FIG. 6B, shown is aphotovoltaic cell comprising plurality of micrometer(s) ornanometer(s)-scaled trapezoidal 610 formed on the supporting substrate600 (after having groove). Only differences in FIG. 6B as compared withthat of FIG. 6A is that the top 612 is opened and receives the portionof the light 604. Similar to FIG. 6A, this case also surface area ofjunction for receiving the light 604 is increased due to reduction ofthe photo-generated carrier recombination, increasing the surface area,basically increasing the more flux too incident, and absorption of allphoto-flux incident on the surface and thereby increasing the conversionefficiency.

According to a preferred embodiment illustrated in FIG. 6C, shown is aphotovoltaic cell comprising plurality of micrometer(s) ornanometers)-scaled trapezoidal 610 formed on the supporting substrate600 (after having groove). Only differences in FIG. 6C as compared withthat of FIG. 6B, is that the gap 614 is opened and receives the portionof the light 604. As mentioned earlier, based on the height h of thetrapezoids and the side angle, the incident light 604 incident on to thegap located in between two trapezoids (e.g. 610 and 616), isconcentrated and increase the conversion efficiency. Similar to FIGS. 6Aand 6B this case also surface area (corresponding to the junction area)for receiving the light 604 is increased due to reduction of thephoto-generated carrier recombination, increasing the surface area,basically increasing the more flux too incident, concentrating incidentlight, and absorption of all photo-flux incident on the surface andthereby increasing the conversion efficiency.

Apparent advantage of this invention as shown in FIGS. 6A, 6B, and 6C,over conventional photovoltaic cells is directly associated with thefact that, unlike conventional photovoltaic cells, large portion of thepn-junctions are used for collecting all photo generated carrierscreated in the electronic material 602, no matter where they aregenerated, the distance the photo generated carriers have to diffuse toreach the pn-junctions created on the surface of the pyramids (601) ortrapezoidal (610) is within the range of the diffusion length of thecarriers and independent to the location where they are generated.Furthermore, for all photo generated carriers in the pyramids (601) ortrapezoidal (610), no matter where they are generated, the distance thephoto generated carriers have to diffuse to reach pn-junctions is withinthe range of the diffusion length of the carriers. Selecting height hand the base m of the pyramids (601) or trapezoidal (610), all carriersgenerated inside semiconductor can be collected. According to thisinvention, the recombination can be made to zero (ideally) and allphoton flux can be absorbed (ideally), and the conversion efficiency canbe made to ˜100% and even >50% using of the Si. On the other hand, asexplained in the description for the prior art shown in FIG. 1, inconventional photovoltaic cells where pn-junctions are perpendicular tothe direction to which incident light travels, the photo generatedcarriers generated in region far away from pn-junctions need to diffusemuch longer distance (diffusion-length) than that for the photogenerated carriers generated near the pn-junctions, thus they have agreater chance to recombine without contributing to photovoltaiceffects. Therefore in this invention, PCCE is expected to be much higherthan that in conventional photovoltaic cells. In addition, it is evidentthat the total effective area that contributes to photovoltaic effect inthis invention can be increased significantly a few orders (>3000)considering 300 mm diameter substrate, 500 μm height rods having 50 nmdiameter and 50 nm pitch.

According to this invention, in way of an example not way of limitation,the supporting substrate 600 can be n-type or p-type Si of <100>orientation, on which the pyramids (601) or trapezoidal (610) can beformed by using the process of patterning using the standardphotolithographic technique, and wet etching using of KOH solution. Thedopants of opposite type of substrate can be diffused into the surfaceof the pyramids (601) or trapezoidal (610) to form the electronicmaterial 602 of Si p-type. Conformal deposition of the dielectricmaterial (not shown) can be done for planarization, and in this casesilicon oxide or polymer can be used. Without dopant diffusion, theelectronic material 602 can be separate Si-epitaxial growth to make thejunction with the Si-substrate. According to this invention, in a way ofan example not way of limitation, the supporting substrate 600 can beGe, GaAs, InP, GaN, ZnO, CdTe, or any suitable semiconductor substrateetc. In which pyramids 601 or trapezoidal 610 can be formed.Alternatively, the supporting substrate 600 can be polymer material,metal (e.g. copper) on which semiconductor can be deposited or formedeither by deposition or electrolytic way, ad the pyramid 601 andtrapezoidal 610 are formed o the substrate prior to formation ofsemiconductor on it.

According to a preferred embodiment illustrated in FIG. 7A, shown is aphotovoltaic cell comprising plurality of micrometer(s)-scaledtrapezoidal 710 formed on the supporting substrate 700 (after havinggroove). The micrometer(s)-scaled trapezoid 710 can have metallicelectrical conduction, p-type or n-type semiconductor electricalconduction. The micrometer(s)-scaled trapezoids are further surroundedby an electronic materials 718 and 720 having metallic electricalconduction, p-type or n-type semiconductor electrical conduction. Theelectronic materials 718 and 720 can be separated material orelectronics materials of p or n type formed into the substrate 700. Theelectronic materials 718 and 720 having the junction of 702 are furtherelectrically connected to electrodes 703 a and 703 b, respectively. Theelectrode 703 a and 703 b are intended to serve as common electrode thatconnects all trapezoids 710. The electrode 703 a is provided for theelectronic material or junction 702. The electrode 703 a can betransparent (not shown here) and can be formed on the electronicmaterial or junction 702. The interface between the micrometer scaledtrapezoids 710 and the electronic material (or junction) 702 form pn- orSchottky junctions where built-in potential for both electrons and holesis generated. According to this invention, the substrate 700 act as thecarrier substrate for making the trapezoids 710. The substrate can beglass, metal, ceramics, polymer, or semiconductor. Alternatively,according to this invention, the carrier substrate can be the solidmetal or metal foils (not shown here). In that case, the substrate 700and the common electrode 703 b can be the one material.

According to this invention, alternatively the micrometer(s)-scaledtrapezoids 710 can be formed on utilizing the semiconductor substrate(not shown here), and the electrode 703 b can be formed on back side ofthe substrate to have common contact for each micrometer(s)-scaledtrapezoids 710, necessary for creating wide surface area. In way of anexample not way of limitation, the nanometer(s) or micrometer(s)-scaledtrapezoids 710 can be made of n-type semiconductor substrate and thethin film material that on or surrounds the micrometer(s)-scaledtrapezoids 710 can be made of p-type semiconductor.

Incident light 704 enters the photovoltaic cell through either theelectrode 703 b (not shown here) or on to the top electrode 703 a. (InFIG. 7A, the incident light enters the photovoltaic cell through theelectrode 703 a). The incident light 704 travels through trapezoids 710electronic materials 718 and 720 (n or p-type) or junction 702, and thesubstrate 700. As the incident light 704 travels through themicro-scaled trapezoids 710, and electronic materials 720 and 718,junction 702, a numerous number of electrons (not shown here) aregenerated in the region near the electrode 703 a. Portion of light 704which passes through the opening portion located in between twotrapezoids (e.g. 710 and 716) where the electronic material 707 is usedfor passivation or make the junction in between micro-scaled trapezoids710 are traveled through the electronic materials 718 and 720, junction702 and the supporting substrate 700 and generates electrons (not shownhere). Some of which generated closer to electronic material junction702 are collected and some of which are generated in the region far from702 or in the passivation layer 707, are recombined and lost. It shouldbe pointed out that electrons are apparently generated all over theregion along the thickness of the electric material (718 and 720) orjunction 702. In addition, as the incident light 704 travels through themicrometer(s)-scaled trapezoids 710, a numerous number of holes (notshown here) are generated in the trapezoids 710. Photo-generatedelectrons generated in the electronic materials (718 and 720), junction702, passivation 707, and substrate 700 diffuse toward pn-junctions 702,created at the interface between the electronic materials 718 and 720,and also at the interface between the electronic material 702 andsubstrate 700. At the pn-junctions, the electrons and the holes areswept away by built-in potential, thus photovoltaic effects set in. Asmentioned earlier, beam 704 incident on to the tilted surface 708 willhave almost the intensity closer to the solar spectrum. As the surfacearea is increased due to utilize of the trapezoids structure, theconversion efficiency is increased. Light incident onto the to the gaps714 located in between two trapezoids structures for example 710 and716, beam is concentrated and increase the carrier generation. The beamconcentration is also expected for the beam incident onto the tiltedsurface 708 is also expected as the surface area increases per fixedbase area.

Unlike conventional solar cell, the solar cell, as shown in FIG. 7A, haspn-junction in the regions of all tilted sides 708 of the trapezoids 710(and 716), the gap 714 created in between two trapezoids (e.g. 710 and716). The pn-junction formed on the side 708 of trapezoids having heighth has surface area, dependent on the height h of the trapezoids 710. Thelight 704 travels perpendicular to the direction of the cell andincident onto the to flat surface 712, tilted side 708, and the gap 714.The intensity of the light incident on to the top flat surface 712 issame as that of the original light intensity l of 704. Light incidentonto the tilted surface 708 and open gap 714 have the intensity morethan the intensity l, due to the self concentrating by the cellstructure and it explains as follows. When the light perpendicularlyincident to the tilted side 708 of the trapezoids, and some of the lightnot shown is reflected and portion of light is transmitted into thepn-junction, not show here (for details see FIGS. 3C and 3D). The lightcomponent from other trapezoids also reflected back and some portion istransmitted from nearest trapezoids tilted side 9 not shown here). It isestimated that light beam transmitted into the tilted side can be mademore than 0.85 times of the original intensity of the light afteroptimizing the structure especially height h and angle α. Based on theside surface area increases per fixed area, the light intensity can beconcentrated and amplified if we compare with the base area. The light704 travels perpendicularly and incident on to the gap 714 has severalcomponents of light in addition to the light (l) incidentperpendicularly. Other components (not shown here) are the reflectedlight components originated from the tilted side 708 of nearesttrapezoids. Based on the aspect ratio (ratio of the height to gap of thetrapezoids), the light incident onto the gap 74 (see 328 of FIG. 3D) canbe enhanced or multiplied. According to this invention, the structurecan be trapezoidal, cylindrical, pyramid etc. and they can be a part ofthe substrate or building block onto the substrate.

According to this invention the light intensity incident onto thesurface top, tilted, and gap, they are concentrated and they can beabsorbed. The carriers generated by the all light component (not shownhere) can be collected without recombination (ideally). It is apparentthat utilizing the solar cell as shown in FIG. 7A can (i) reduce therecombination, (ii) increasing the surface increasing the more intensityfor the fixed base area, and (ii) absorb all photo flux as transmittedto the semiconductor, thereby increasing the conversion efficiency.

According to this present invention, alternatively the top electrode 703a can be made directly onto the top of the electronic material 720. FIG.7B shows the schematic representing the photovoltaic cell according tothis invention, wherein, the same numeral represent the same parts asexplained in FIG. 7A, and repeated explanation is omitted here. Thedifference in FIG. 7B as compared to FIG. 7A is that, the electrode madeonto the electronic material 720 in all sides, for example top 712tilted side 708, and the gap 714.

The photovoltaic cell explained in FIGS. 7A and 7B, are based onto theelectronics materials 718 and 720 which can be based on the radiationtolerant materials for example CdS, CdTe etc. If those material ormaterial systems which are not highly tolerant under radiation materialsystems such as Si, Polymer, GaAs, etc. are used, then the radiationtolerant material is to be needed to prevent the photovoltaic celldamage from radiation. According to this invention, at least one layerfor example 722 (shown in FIG. 7C) is to be needed onto the top of thephotovoltaic cell to prevent the photovoltaic cell from damaging due tothe radiation. The additional layer 722 is made onto the top of thephotovoltaic cell. The layer will reduce and/or completely alleviate theradiation dose exposing directly onto the photovoltaic cell. Thedifference in FIG. 7C as compared to FIG. 7B is that an additional layer722 is used to protect from the radiation exposure.

According to this invention, the photovoltaic cell can be made to havemore than one junction. FIG. 7D is the schematic showing ancross-sectional view of photovoltaic cell wherein the same numerals arethe same parts as explained in FIGS. 7A, 7B, and 7C, so that repeatedexplanation is omitted here. The top junction formed by the additionalelectronic material 724, can be flat and the second junction 702 canhave larger surface area, as explained in FIGS. 6A, 6B, 7A, 7B, and 7C.The top junction formed by the electronic material 724 can absorbcomparatively lower wavelength light and longer wavelength lights areabsorbed by the second junction 702. In this way, the broad ranges ofsolar spectrum can be possible and the conversion efficiency can befurther increased, according to this invention. Alternatively, type oftop layer material 724 can be either electronic material to create thesemiconductor junction or the material having high radiation tolerantfor the case of the photovoltaic cell for space application. Thedifference ire FIG. 7D, as compared to FIG. 7C, is that addition layer724 is used either for creating an another junction to extend the solarspectrum absorption or to prevent the photovoltaic cell from theradiation exposure. Alternatively, more than two junctions utilizing thecombination of flat and grooved junctions can also be used according tothis invention.

According to this invention, explained in FIGS. 7A, 7B, 7C, and 7D, thesubstrate 700 can be act as the carrier substrate for creating thestructures of trapezoids, pyramid, cylindrical etc. to have largersurface area (and also larger junction area). The type of substrate canbe semiconductor, polymer, ceramic, solid metal, metal foil. In the caseof the semiconductor using as carrier 700, a layer of dielectricmaterial may be required to isolate the photovoltaic cell andsemiconductor current injection or leaking (not shown here). If thesolid metal or metal foil is used as the carrier substrate than themetal (used as the carrier substrate) can be also used one of the commonelectrode (or contact). If the ceramics or polymer is used as thecarrier substrate is used, the structures of trapezoids, cylindrical, orpyramid etc. can be made on the substrate using molding, casting,etching, or printing technology.

According to this invention. alternatively, structures of trapezoids,cylindrical, or pyramid of same or different type of material can bemade onto the carrier substrate by a process or transferring thepre-formed structures on foreign substrate (not shown here) aretransferred to the substrate (700) acting as the carrier substrate.

In an alternative preferred embodiment shown in FIG. 8, a photovoltaiccell comprises plurality of micro or nanometer(s)-scaled trapezoidal orcylinder 801 are electrically connected to a substrate 800. The cylinderor trapezoidal 801 can have metallic electrical conduction, p-type orn-type semiconductor electrical conduction. The dielectric layer 812 onthe substrate 800 isolate the cylinder or trapezoidal shaped rods. Themicro or nanometer(s)-scaled trapezoidal or cylinder 801 are furthersurrounded by an electronic materials 818 and 820 having metallicelectrical conduction, top and bottom contacts 803 a and 703 b. Theelectronic materials 818 and 820 form p-type or n-type semiconductorelectrical junction 822. The electronic materials 818 and 820 can beseparated material or electronics materials of p or n type formed insideor on 801 and 800. The electronic materials 818 and 820 are furtherelectrically connected to electrodes 803 a and 803 b, respectively. Theelectrodes 803 a and 803 b are intended to serve as common electrodesthat connects all cylinder or trapezoidal shaped electrical junction822. The electrode 803 a is on the electronic material 820. Theinterface between the nanometer(s)-scale tubes 818 and the electronicmaterials 820 form pn- or Schottky junctions 822, thus there are pn- orSchottky junctions on both sides, inside and outside, of the micro ornanometer(s)-scale trapezoidal or cylindrical rod 801.

According to this invention, alternatively the nanometer(s) ormicrometer(s)-scale tubes, wires or trapezoids, 801 can be formed on thesubstrate (not shown here), and the electrode 803 a can be made on thesubstrate to have a common contact for each nanometer(s)-scale rods 801,necessary for creating junction.

In way of an example not way of imitation, the micro ornanometers(s)-scale trapezoidal or cylindrical rod 801 can be made ofmetal and the electronic materials 818 and 822 that surrounds or aroundthe micro or nanometer(s)-scale trapezoidal or cylindrical rod 801 canbe made of p-type semiconductor, thus the interface of 818/822 formspn-junctions in micro or nanometer(s)-scale trapezoidal or cylindricalrod 801. Incident light 804 enters the photovoltaic cell through theelectronic materials 820 (front-side of the cell). As the incident light804 travels through the electronic material 820, numerous numbers ofelectrons (not shown here) are generated. It should be pointed out thatelectrons (of electron-hole pairs) are apparently generated all over theregion along the thickness of the nanometer(s) or micrometer(s)-scaleblocks (e.g. rods) 801 and also the gaps 814 in between blocks 801.Photo-generated electrons in the electronic materials 818 and 820 madeof p and n-type-type semiconductors, then diffuse toward pn-junctions822 in the interface of 818/820. At the pn-junctions, the diffusedelectrons are swept away by built-in potential, thus photovoltaiceffects set in.

Common advantages already described for the photovoltaic cell in FIGS. 6and 7, can be achieved in this invention. Only difference of forming thenano or micro-scaled blocks which are formed without forming thegrooves.

According to this invention, in way of an example not way of limitation,the supporting substrate 800 can be Si substrate, on which trapezoidalor slanted cylinder can be made by conventional photolithographyfollowed by wet etching using standard etchant (e.g. KOH solution). Inorder to isolate the slanted trapezoidal, dielectric layer of siliconoxide can be used. Different type of thin-films of p-type and n-type canbe deposited on the slanted cylinder 801 after uniformly metallizationto form the electrode 803 b The thin films could be any suitable thinfilms which could form the junction. For example, they are thecombination of CdTe/CdS, Zn(Cd)Te/Zns, ZnO based materials, Si basedalloyed material (e.g. Si:Ge or a-Si), GaAs or InP based alloyedmaterials etc. Conformal deposition of the electronic material can bedone based on the slant angle and planarization (not shown here) can bemade by depositing the passivation layer (polymer or silicon oxide).

According to this invention, in way of an example not way of limitation,the supporting substrate 800 can be Ge, GaAs, GaN, InP, GaN, CdTe, orZnO.

In an alternative preferred embodiment shown in FIG. 9, a photovoltaiccell comprises plurality of micro-meter(s) scaled pyramid or trapezoidal801 are electrically connected to a substrate 900. The micro-meter(s)scaled pyramid or trapezoidal 901 are further surrounded by anelectronic materials 918 and 920 having metallic electrical conduction.The electronic materials 918, 920, and 924 and the supporting substrate800 are further electrically connected to electrodes 903, respectively.The micro-meter(s) scaled pyramid or trapezoidal-shaped has top surfacewith electronic material of 924 can form the have metallic electricalconduction, with suitable electrolyte solution (not shown). Forcollecting the charge from the electrolyte, another electrode is placedin the electrolyte (not shown here).

The structures to increase the surface area (equivalent to the junctionarea) can be made alternatively by using the nano-blocks of having fewnanometer sizes, the quantum confinement effect is possible. Absorptionof broad solar spectrum can be possible utilizing the different sizesand different semiconductor nano-scaled blocks.

Apparent advantage of this invention over conventional photovoltaiccells is directly associated with the fact that, unlike conventionalphotovoltaic cells, at least one junction having larger surface area andalso have the capability of self concentration as explained in FIGS. 2to 5 are created for increasing the carrier generation and also forcollecting all photo generated carriers created in the absorption layer,no matter where they are generated. According to this invention, therecombination can be made to zero (ideally) and all photon flux can beabsorbed (ideally), and the conversion efficiency can be made to ˜100%and even >50% using of the Si. On the other hand, as explained in thedescription for the prior art shown in FIG. 1 in conventionalphotovoltaic cells where electrical-junctions are perpendicular to thedirection to which incident light travels, the photo generated carriersgenerated in region far away from electrical-junctions need to diffusemuch longer distance (diffusion-length) than that for the photogenerated carriers generated near the junctions, thus they have agreater chance to recombine without contributing to photovoltaiceffects. Therefore in this invention, PCCE is expected to be much higherthan that in conventional photovoltaic cells for specific wavelength. Inaddition, it is evident that the total effective area that contributesto photovoltaic effect in this invention can be increased significantlya few orders (>3000) and also the light incident onto the gap in betweentwo structures have the concentrating light. Both effects will increasethe carrier generations and thereby increase the conversion efficiency.

According to this invention, in way of an example not way of limitation,the supporting substrate (600, 700, 800, or 900) can be ceramics, glass,polymer or any kind of semiconductor on which transparent ornontransparent metal contact (603 b, 703 b, or 803 b) is made.Alternatively, supporting substrate (600, 700, 800, or 900) can be metalwhich also acts the metal contact. For this case, copper, stainlesssteel, Aluminum, alloyed metal, or their thin metal foil, can be used.According to this invention, the nano or micro structured of trapezoidscylinder, or pyramid, can be any kind of semiconductor or compoundsemiconductors, having the absorption capability in the desired spectrumregion. They could be Si, Ge, InP, GaAs, CdSe, CdS, CdTe, ZnO, ZnTe,ZnCdTe, CuInSe, CuSe, InGaAs.

According to this invention, the nano or micro scaled structures couldbe GaN materials (n or p type) and the dozens of the materials could beIn_(1-x)Ga_(x)N (p or n type, opposite to GaN rods). With increasing ofthe Ga contents, the band-gap of InGaN can be increased to close to ˜3.4eV which is same as that of the GaN. With increasing of the In contentsin InGaN, the band gap can be reduced to ˜0.65 eV. Photons with lessenergy than the band gap slip right through. For example, red lightphotons are not absorbed by high-band-gap semiconductors. While photonsenergy higher than the band gap are absorbed—for example, blue lightphotons in a low-band gap semiconductor—their excess energy is wasted asheat.

According to this invention, alternatively the, nano or micro scaledstructures could be III-V based materials (n or p type) for example InPand the dozens of the materials could be III-V based material forexample In_(1-x)Ga_(x)As (p or n type, opposite to InP rods). In thiscase, with adjusting of in contents, band gap can be tuned and therebythe wide spectrum of the solar energy can be absorbed.

According to this invention, alternatively nano or micro scaledstructures could be II-V based materials (n or p type) for example CdTeand the dozens of the materials could be II-VI based material forexample CdZnS (p or n type, opposite to CdTe rods) or Zn(Cd)Te/ZnS basedmaterials. In this case, with adjusting of Zn contents, band gap can betuned and thereby the wide spectrum of the solar energy can be absorbed.

According to this invention, alternatively nano or micro scaledstructures, could be Si (or amorphous Silicon materials (n or p type)and the dozens of the materials could be Si: Ge alloy (p or n type,opposite to Si rods). In this case, with adjusting of Ge contents, bandgap can be tuned and thereby the wide spectrum of the solar energy canbe absorbed.

According to this invention, alternatively nano or micro scaledstructures could be Si, InP, or CdTe (n or p type) and the dozens of thematerials, could be different material which could make the junctionwith the rods (wires or tubes) and each type of material has thespecific band gap for absorbing the specific range of solar spectrum. Inthis way also wide range of solar spectrum can be absorbed, and withincreasing of the junction area (due to use of the rods, wires, ortubes), the electrical power generation could be increased tremendously50 times and beyond.

According to this invention, the nanoparticles or nanometer(s)-scalewires, mentioned in the preferred embodiments, can be any kinds ofelectronics materials covering semiconductor, insulator or metal.

According to this invention, nano or micro scaled structures can be madefrom the semiconductors such as Si, Ge, or compound semiconductors fromIII-V or II-VI groups. As an example for rods, wire, or tubes, InP,GaAs, or GaN III-V compound semiconductor can be used and they can bemade using standard growth process for example, MOCVD, MBE, or standardepitaxial growth. According to this invention, the self-assembledprocess can also be used to make wires, rods, or tubes and their relatedpn-junction to increase the junction area. These rods, wire, or tubescan be grown on the semiconductors (under same group or others),polymers, or insulator. Alternatively, according to this invention,these rods, wire, or tubes, can be transferred to the foreign substrateor to the layer of foreign material. The foreign substrate or the layerof material can be any semiconductor such as Si, Ge, InP, GaAs, GaN,ZnS, CdTe, CdS, ZnCdTe, HgCdTe, etc. The substrate can cover also allkinds of polymers or ceramics such as AlN, Silicon-oxide etc.

According to this invention, nano or micro scaled structures based onII-VI compound semiconductor can also be used. As an example CdTe, CdS,Cdse, ZnS, or ZnSe can also be used, and they can be made using standardgrowth process for example, sputtering, evaporation, MOCVD, MBE, orstandard epitaxial growth or chemical syntheses. According to thisinvention, the self-assembled process can also be used to make nano ormicro scaled structures, and their related pn-junction to increase thejunction area. These rods, wire, or tubes can be grown on thesemiconductors (under same group or others), polymers, or insulator.Alternatively, according to this invention, these rods, wire, or tubes,can be transferred to the foreign substrate or to the layer of foreignmaterial. The foreign substrate or the layer of material can be anysemiconductor such as Si, Ge, InP, GaAs, GaN, ZnS, CdTe, CdS, ZnCdTe,HgCdTe, etc. The substrate can cover also all kinds of polymers orceramics such as AlN, Silicon-oxide etc.

According to this invention, nano or micro scaled structures can be madefrom the carbon type materials (semiconductor, insulators, or metal likeperformances) such as carbon nano-tubes which could be single, ormultiple layered. They can be made using standard growth process forexample, MOCVD, MBE, or standard epitaxial growth. According to thisinvention, the self-assembled process can also be used to make wires,rods, or tubes and their related pn-junction to increase the junctionarea. These tubes can be grown on the semiconductors (under same groupor others), polymers, or insulator. Alternatively, according to thisinvention, these rods, wire, or tubes, can be transferred to the foreignsubstrate or to the layer of foreign material. The foreign substrate orthe layer of material can be any semiconductor such as Si, Ge, InP,GaAs, GaN, ZnS, CdTe, CdS, ZnCdTe, HgCdTe, etc. The substrate can coveralso all kinds of polymers or ceramics such as AlN, Silicon-oxide etc.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting. Therefore, reference to thedetails of the preferred embodiments is not intended to limit theirscope. Although the invention has been described with respect tospecific embodiment for complete and clear disclosure, the appendedclaims are not to be thus limited but are to be construed as embodyingall modification and alternative constructions that may be occurred toone skilled in the art which fairly fall within the basic teaching hereis set forth.

Although the invention has been described with respect to specificembodiment for complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodification and alternative constructions that may be occurred to oneskilled in the art which fairly fall within the basic teaching here isset forth.

The present invention is expected to be found practically use not onlyin the novel photo-voltaic cells which as higher power generationcapability (25 times and beyond) as compared with that of theconventional cells, but also other photonics devices such asphotodetector, lighting devices etc. The proposed invention can be usedfor fabricating for photonics devices (e.g. wide solar panel) for bothcommercial and space applications.

What is claimed is:
 1. A photovoltaic cell comprising: a substratehaving a top surface; wherein said top surface of the substrate has athree-dimensional geometric pattern etched from the substrate, saidsubstrate being a single piece of material; wherein thethree-dimensional geometric pattern comprising, an array of pyramidal,conical, truncated pyramidal, or truncated conical shaped nano-scaled ormicrometer-scaled protruding structures separated by gaps, wherein eachprotruding structure has tilted sides, a base, an internal angle alphabetween the tilted sides and the base, and a height, wherein the gapsseparate the bases of the protruding structures, wherein the bases ofthe protruding structures are oriented such that the bases of theprotruding structures are coplanar or parallel, wherein the internalangle alpha of each protruding structure is between 45 and 90 degrees,thereby concentrating some light incident on the tilted sides of eachprotruding structure onto the gaps between the protruding structures,and wherein the height of each protruding structure, the internal anglealpha of each protruding structure, and the gaps between the protrudingstructures are oriented to reflect some light incident on the tiltedsides of each protruding structure back and forth between the tiltedsides of adjacent protruding structures; an electrode, wherein theelectrode completely overlays said three-dimensional geometric patternetched from the substrate; and a pn junction, wherein the pn junctionoverlays the electrode.
 2. The photovoltaic cell of claim 1, furthercomprising a radiation tolerant layer.
 3. The photovoltaic cell of claim1, wherein the pn junction is electrically connected to the electrode.4. The photovoltaic cell of claim 1 wherein the electrode provides athree-dimensional geometric pattern that follows the contour of thethree dimensional geometric pattern of the top surface of the substrate.5. A photovoltaic cell comprising: a substrate formed from asemiconductor material; wherein a three-dimensional geometric patternetched from the substrate, has a top surface and wherein said substratebeing a single piece of material; a first electrode, wherein the firstelectrode completely overlays said three-dimensional geometric patternetched from the substrate; wherein a top surface of the first electrodeprovides a three dimensional geometric pattern that follows the contourof the three dimensional pattern etched from the substrate, a firstelectrical material of p- or n-type, overlying the first electrode; asecond electrical material of type opposite to that of the firstelectrical material, completely overlying the first electrical materialthereby providing a p-n junction along the interface between the firstelectrical material and the second electrical material; wherein a topsurface of the first electrical material provides a three dimensionalgeometric pattern that follows the contour of the three dimensionalgeometric pattern of the top surface of the first electrode, and asecond electrode, overlying the second electrical material, wherein thethree-dimensional geometric pattern etched from the substratecomprising, an array of pyramidal, conical, truncated pyramidal, ortruncated conical shaped nano-scaled or micrometer-scaled protrudingstructures separated by gaps, wherein each protruding structure hastilted sides, a base, an internal angle alpha between the tilted sidesand the base, and a height, wherein the gaps separate the bases of theprotruding structures, wherein the bases of the protruding structuresare oriented such that the bases of the protruding structures arecoplanar or parallel, wherein the internal angle alpha of eachprotruding structure is between 45 and 90 degrees, thereby concentratingsome light incident on the tilted sides of each protruding structureonto the gaps between the protruding structures, and wherein the heightof each protruding structure, the internal angle alpha of eachprotruding structure, and the gaps between the protruding structures areoriented to reflect some light incident on the tilted sides of eachprotruding structure back and forth between the tilted sides of adjacentprotruding structures.
 6. The photovoltaic cell of claim 5, furthercomprising a passivation material that overlays the second electrode andforms a level surface.
 7. The photovoltaic cell of claim 5, furthercomprising a radiation tolerant layer.
 8. The photovoltaic cell of claim5, wherein said first electric material and said second electricalmaterial are selected from the group consisting of Si, CdTe, GaAs, InP,Ge, ZnO, SiGe, GaSb, CdZnTe, InSb, HgCdTe, and GaN.
 9. The photovoltaiccell of claim 5, wherein the second electrical material provides a threedimensional geometric pattern that follows the contour of the threedimensional geometric pattern of the top surface of said firstelectrical material.
 10. The photovoltaic cell of claim 5, wherein thesecond electrode forms a level surface.
 11. The photovoltaic cell ofclaim 5, wherein the second electrical material forms a level surface.12. The photovoltaic cell of claim 5 wherein the pn junction comprisesmultiple pn junctions.
 13. A photovoltaic cell comprising: a substrate;wherein a three-dimensional geometric pattern etched from the substrate,has a top surface and wherein said substrate being a single piece ofmaterial; a first electrode, wherein the first electrode completelyoverlays said three-dimensional geometric pattern etched from thesubstrate; wherein a top surface of the first electrode provides a threedimensional geometric pattern that follows the contour of the threedimensional pattern etched from the substrate, a first electricalmaterial of p- or n-type, overlying the first electrode; wherein a topsurface of the first electrical material provides a three dimensionalgeometric pattern that follows the contour of the three dimensionalgeometric pattern of the top surface of said first electrode, a secondelectrical material of type opposite to that of the first electricalmaterial, completely overlying the first electrical material therebyproviding a p-n junction along the interface between the firstelectrical material and the second electrical material; wherein a topsurface of the second electrical material provides a three dimensionalgeometric pattern that follows the contour of the three dimensionalgeometric pattern of the top surface of said first electrical material,a passivation material that fills in between the three-dimensionalgeometric pattern of the top surface of the second electrical materialand forms a level surface; a third electrical material disposed on thepassivation material is electrically connected to the second electricalmaterial; a second electrode overlying the third electrical materialwherein the second electrode is electrically connected to the thirdelectrical material; wherein the three-dimensional geometric patternetched from the substrate comprising, an array of pyramidal, conical,truncated pyramidal, or truncated conical shaped nano-scaled ormicrometer-scaled protruding structures separated by gaps, wherein eachprotruding structure has tilted sides, a base, an internal angle alphabetween the tilted sides and the base, and a height, wherein the gapsseparate the bases of the protruding structures, wherein the bases ofthe protruding structures are oriented such that the bases of theprotruding structures are coplanar or parallel, wherein the internalangle alpha of each protruding structure is between 45 and 90 degrees,thereby concentrating some light incident on the tilted sides of eachprotruding structure onto the gaps between the protruding structures,and wherein the height of each protruding structure, the internal anglealpha of each protruding structure, and the gaps between the protrudingstructures are oriented to reflect some light incident on the tiltedsides of each protruding structure back and forth between the tiltedsides of adjacent protruding structures.
 14. The photovoltaic cell ofclaim 13 wherein the third electrical material is of type opposite tothe second electrical material.
 15. The photovoltaic cell of claim 13,further comprising a radiation tolerant layer.
 16. The photovoltaic cellof claim 13, wherein said first electric material is selected from thegroup consisting of Si, CdTe, GaAs, InP, Ge, ZnO, Si:Ge, GaSb, CdZnTe,InSb, HgCdTe, and GaN.
 17. The photovoltaic cell of claim 13, whereinthe first and second electrical material is electrically connected toeither the first or second electrode.
 18. The photovoltaic cell of claim13 wherein the third electrical material creates a junction that extendsthe range of solar spectrum absorption or to prevent the photovoltaiccell from the radiation exposure.
 19. The photovoltaic cell of claim 13,wherein the pn junction comprises multiple pn junctions.